Just like Jibi said, open the .bat file for the simulator you are using (eg. 8700c.bat) in notepad, and change the PIN value to be whatever you want.

In answer to your second question, you can and can't use the simulator like a real BlackBerry. It will only work with a BES, not Redirector or BIS. Assuming you have Outlook setup and installed on the computer that you will use the simulator on, add that user to the BES, then start up the simulator. There is an option to "simulate USB connection". With Desktop Manager started, simulate this connection. It should get picked up in desktop manager and act just like a real BlackBerry (even if you still have the 2100000 PIN associated with it). Once it's gone through it's activation process, you'll be able to send/receive emails on it as long as desktop manager is opened and therefore it's using the serial bypass function with the simulated USB connection.

Now, a note on this...the simulators can be touchy at times. I've had weeks where no matter what I do, the USB connection will not establish and therefore no serial bypass...but then all of a sudden it'll work for me. YMMV.